1. Technical Field
This invention relates generally to a method for automatically shifting a manual transmission, and more particularly to such a method that is applicable to synchromesh transmissions.
2. Background Art
Synchromesh transmissions are used on virtually all current models of cars equipped with manual transmissions, and are commonly found on other machines wherever the shifting of gears while moving is required. Synchromesh transmissions use friction to bring drive gears to the same speed as an output shaft before engagement. Typically, a synchronizer assembly, rotationally fixed with respect to the output shaft, is moved axially along the output shaft until it comes in frictional contact with a selected drive gear. Friction between a collar or sleeve of the synchronizer and the selected drive gear is used to synchronize the speed of the selected drive gear with the output shaft.
Several approaches have been proposed to automate the gear change process in synchromesh transmissions using actuators to provide the motive power required to move clutch and/or transmission elements. For example, U.S. Pat. No. 6,295,884 granted on Oct. 2, 2001 to Miyake, et al. for a CONTROL METHOD AND CONTROL APPARATUS FOR GEAR TRANSMISSION, describes a control methodology for synchromesh transmissions that uses a predetermined cutoff throttle to shift at a variable rate based on vehicle characteristics. The speed of change linearly increases with throttle angle. Shift speed is varied in different regimes of the gear engagement process, for example, a longer speed change during synchronization and a shorter speed time during sleeve engagement. However, Miyake, et al. does not disclose the method by which the varying times are determined.
A control device for automated synchromesh transmissions is disclosed in U.S. Pat. No.6,393,928 grated May 28, 2002 to Shinji Watanabe for a CONTROL DEVICE FOR SYNCHROMESH AUTOMATIC TRANSMISSION. The Watanabe control device senses a calibrated linear and angular position of the shift fork. The shift fork position required to achieve a selected position between every shift is learned and stored. The rate at which shift changes are made is derived empirically and is tuned/learned for optimal performance throughout the life of the transmission. The control device proposed by Watanabe requires shift position sensors and does not provide for modulation of the clutch to help speed matching.
Another device for controlling the shift process in automated synchromesh transmissions is disclosed in U.S. Pat. No. 6,422,104 granted Jul. 23, 2002 to Mitsutoshi Kamiya for an APPARATUS FOR SELECTING SELECTION GATE POSITIONS FOR CHANGE SPEED IN AUTOMATIC GEAR TRANSMISSION. Kamiya describes a mechanical and switch arrangement for the gear shift process that uses switches and interlocks for sequencing the control of the shift fork linear and rotor actuators. However, Kamiya requires a number of hard sensors and provides no means to minimize the synchronization time.
The present invention is directed to overcoming the above described problems associated with current methods for automatically shifting synchromesh transmissions. It is desirable to have a method for quickly shifting a synchromesh transmission that provides good shift feel and minimizes wear on transmission components while simultaneously minimizing drive train wind-up. It is also desirable to have a method for automatically shifting a synchromesh transmission that does not require extrinsic, supplemental, or auxiliary sensors, such as shift fork position sensors, which add cost and complexity to the transmission control system. Moreover, it is desirable to have a method for automatically shifting a synchromesh transmission that controls engine throttle during the shift process to dampen drive train oscillations and thereby reduce the length of time required for the synchronization process.